We present an experimental study on mixed-mode crack propagation in thin sheet specimens of a soft silicone elastomer. To introduce mixed-mode loading, we adopted the widely applied pure shear fracture testing geometry, but oriented the initial crack at an inclined angle relative to the direction perpendicular to the external tensile loading. Because of the inclined angle, locally the crack tip was subjected to both tensile and shear loading even though the global loading was tensile, thus resulting in a mixed Mode-I and Mode-II condition for the crack. Altering the inclined angle led to different degrees of mode-mixity and hence different crack propagation trajectories. Using a particle tracking method, we were able to measure the nonlinear deformation fields throughout the entire course of crack propagation. Based on the measured deformation fields, we used J-integral to calculate the energy release rate during crack propagation and found that the results were insensitive to the tangent direction of the crack trajectory, suggesting that the fracture toughness was approximately mode independent. Moreover, the tangent direction of the crack trajectory, when plotted in the reference configuration, was observed to be perpendicular to the direction of maximum principal stretch. The experimental results pave the way for establishing quasi-static mixed-mode fracture criteria for soft silicone elastomer, which has not yet been well understood in the literature.

我们对软硅弹性体的薄片试样中的混合模式裂纹扩展进行了实验研究。为了引入混合模式加载，我们采用了广泛应用的纯剪切断裂测试几何形状，但将初始裂纹定向为相对于垂直于外部拉伸加载的方向倾斜的角度。由于倾斜的角度，即使整体载荷是拉伸载荷，裂纹尖端局部也受到拉伸和剪切载荷，从而导致裂纹的模式 I 和模式 II 混合。改变倾斜角会导致不同程度的模式混合，从而导致不同的裂纹扩展轨迹。使用粒子跟踪方法，我们能够测量整个裂纹扩展过程中的非线性变形场。基于测量的变形场，我们使用 J 积分计算裂纹扩展过程中的能量释放率，发现结果对裂纹轨迹的切线方向不敏感，表明断裂韧性近似模态无关。此外，当在参考配置中绘制时，裂纹轨迹的切线方向被观察到垂直于最大主拉伸方向。实验结果为建立软有机硅弹性体的准静态混合模式断裂标准铺平了道路，这在文献中尚未得到很好的理解。表明断裂韧性近似与模式无关。此外，当在参考配置中绘制时，裂纹轨迹的切线方向被观察到垂直于最大主拉伸方向。实验结果为建立软有机硅弹性体的准静态混合模式断裂标准铺平了道路，这在文献中尚未得到很好的理解。表明断裂韧性近似与模式无关。此外，当在参考配置中绘制时，裂纹轨迹的切线方向被观察到垂直于最大主拉伸方向。实验结果为建立软有机硅弹性体的准静态混合模式断裂标准铺平了道路，这在文献中尚未得到很好的理解。